Ask MetaFilter commenters agree: Knowing someone’s name because his boss forces him to wear a name tag does not constitute permission to use that name. Having settled on the consensus that addressing name-tagged employees by their first names is creepy, the commenters attempt to tease out why. Judging by the comments, your age might influence how much you agree with their consensus.

I think that I deviate from most of the Gen XYers on the MF thread. I’ve never worked in customer service, but I always thought it was good to establish rapport with an agent, by looking at the tag, and if it said, “Sally,” to say, “How’s your day going, Sally?” If I’ve got my earbuds in while standing in line, I take one out, because I feel it’s rude to just swipe my card, grab my groceries, and go.